When We configure AAA on Cisco ASA or any IOS device (Router/Switch), it is always a good practice to confirm that the configuration is good and the server is available and responding correctly.

Cisco IOS:

Radius Server IP Address: 10.1.2.3
Username: amolak
Password: password123

ROUTER-1#test aaa group radius server 10.1.2.3 amolak password123 legacy
Attempting authentication test to server-group radius using radius
User was successfully authenticated.

ROUTER-1#test aaa group radius server 10.1.2.3 amolak wrongpassword legacy  
Attempting authentication test to server-group radius using radius
User authentication request was rejected by server.

Cisco ASA:

Radius Servers Group Name: RADIUS-SERVERS
Radius Server IP Address: 10.1.2.3
Username: amolak
Password: password123

ASA-1# test aaa-server authentication RADIUS-SERVERS
Server IP Address or name: 10.1.2.3
Username: amolak
Password: password123
INFO: Attempting Authentication test to IP address <10.1.2.3> (timeout: 12 seconds)
INFO: Authentication Successful

ASA-1# test aaa-server authentication RADIUS-SERVERS
Server IP Address or name: 10.1.2.3
Username: amolak
Password: wrongpassword
INFO: Attempting Authentication test to IP address <10.1.2.3> (timeout: 12 seconds)
ERROR: Authentication Rejected: AAA failure

Note that you can choose the group, or specific server in the group. This makes it possible to check all servers in the group are working.